1. Field of the Disclosure
The disclosure relates generally to apparatuses and methods used in wellbores.
2. Description of Related Art
With reference to FIG. 1, one example of a prior art actuating device is shown therein. A downhole tool 10 is shown disposed in a well bore 5 and tethered or supported by a longitudinal member 12. Longitudinal member 12 may be a wireline, coiled tubing, or jointed drill pipe as is known in the art. As is well known in the art, such downhole tools can be in the form of an elongated apparatus known in the art as a sonde, and the actuating device is disposed within the sonde. The actuating device illustrated in the specific example of FIG. 1 is a clamping device 14. The clamping device 14 comprises a linkage arm 18 pivotally connected to a clamping arm 16. The clamping device 14 operates by angular movement of the linkage arm 18. The linkage arm 18 is powered by a motor 24 via a drive nut 22 and drive screw 20. As shown, the motor provides a rotating force onto the drive screw 20, which by virtue of its threaded connection with the drive nut 22, upwardly motivates the drive nut 22, which in turn moves the linkage arm 18. With regard to this particular application, the sonde is an acoustic device having geophones. As is known in the art, proper operation of the geophones necessitates that the sonde be tightly pressed against one side of the well bore 5.
One of the problems with such prior art devices is the large amount of weight and volume required by the clamping device 14 and its associated hardware. With regard to the clamping device 14 as shown, the motor 24 often occupies a substantial space and can have a large weight. Therefore, there exists a need for the use of downhole actuation devices that can be utilized without the requirements of large weight and/or volume.
In addition, wireline operations are carried out in oil and gas wells for conveying tools downhole in the well. A wide variety of downhole tools may be supported on a wireline including tools to perform logging, perforating, and setting and retrieving operations. The tools typically comprise a combination of different tubular members threaded together to form a working unit which is manipulated and controlled from the surface via the wireline. Although tools may be conveyed downhole on a tubing string which can withstand substantially higher extraction forces than a wireline, oftentimes a wireline is preferred because it saves substantial rig time in conveying tools downhole and positioning them within the well. A cable head, which connects the tools to the wireline, is typically provided with a release mechanism to permit the wireline to be disconnected from the tools, such as when the tools become stuck downhole, or after setting a tool intended to be left downhole.
The commonly accepted safe operational pull of the wireline is a pull which does not exceed one-half the breaking strength of the wireline. When a tension is placed on the wireline which is over 50% of its break point, then problems begin to occur with the electrical conductors in the wireline. Also, there is the danger of breaking the wireline.
A typical wireline release utilizes a mechanical weak point in the connection between the wireline and the cable head. Typically this is a metal member which is designed to break upon a predetermined pull on the wireline. The correct conventional mechanical weak point must be calculated and installed prior to running the cable head and tools into the borehole on the wireline.
There are certain limitations in using the typical mechanical weak point release devices. One is the strength of the wireline itself and the other is the strength of the mechanical weak point. For example, when the tool is stuck, the operator generally fishes for the tool with the wireline still attached to the tool in the wellbore. The operator lowers a grapple on a separate line, such as a slick line, which grabs the top of the cable head or the tool body. The operator attempts to release the wireline from the tool. Removing the wireline makes it easier to pull the tools and pipe out of the wellbore. In order to effect the release, the operator places a large tension on the wireline to activate the mechanical release. If the cable head and tools are in a deviated wellbore, the effects of friction on the wireline may prevent the mechanical link at the cable head from receiving sufficient tension to break the link. In some cases, the wireline may break at some uphole location before the mechanical link breaks. The presence of the broken wireline substantially impairs the fishing operation for the stuck tools.
Various other apparatuses and methods have been provided for releasing the wireline from the cable head and tools. One such method includes the use of a spring set at a selected tension. Once the force on the spring exceeds the selected tension, the wireline is released. This release still requires that the amount of load required to release the wireline be predetermined prior to lowering the cable head into the well. If the spring tension exceeds that selected tension, the cable head can release prematurely.
Another typical release system relies primarily on shear pins or shear screws. The shear pins or screws can have a low failure point because they are exposed to various cyclical forces, which tend to affect their ultimate shear rating. The shear pins or screws are exposed to the fluids in the wellbore which over time can affect the inherent strength of the shear screws or pins, thereby making them susceptible to failure at stresses below their rated failure point. Unexpected release can significantly delay operations, causing additional operating expense. An unexpected release can also result in the loss of downhole tools and in extreme cases can cause severe damage to the wellbore.
When the cable head and tools get stuck in the wellbore and the wireline breaks upon pulling on the wireline with too much tension, fishing operations to retrieve the tools become difficult. Therefore, there is a need for an improved apparatus and method for releasing a tool from a conveying member, such as wireline.